Updated /arbitrary/metadata/* response when not found.

src/main/java/org/qortal/api/resource/ArbitraryResource.java

@@ -737,7 +737,7 @@ public class ArbitraryResource {
 			throw ApiExceptionFactory.INSTANCE.createCustomException(request, ApiError.FILE_NOT_FOUND, e.getMessage());
 		}
 
-		throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_DATA);
+		throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.FILE_NOT_FOUND);
 	}